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  <div class="section" id="data-marshalling-support">
<span id="marshalling-utils"></span><h1>Data marshalling support<a class="headerlink" href="#data-marshalling-support" title="Permalink to this headline">¶</a></h1>
<p>These routines allow C code to work with serialized objects using the same data
format as the <a title="Convert Python objects to streams of bytes and back (with different constraints)." class="reference external" href="../library/marshal.html#module-marshal"><tt class="xref docutils literal"><span class="pre">marshal</span></tt></a> module.  There are functions to write data into the
serialization format, and additional functions that can be used to read the data
back.  Files used to store marshalled data must be opened in binary mode.</p>
<p>Numeric values are stored with the least significant byte first.</p>
<p>The module supports two versions of the data format: version 0 is the historical
version, version 1 (new in Python 2.4) shares interned strings in the file, and
upon unmarshalling.  Version 2 (new in Python 2.5) uses a binary format for
floating point numbers.
<em>Py_MARSHAL_VERSION</em> indicates the current file format (currently 2).</p>
<dl class="cfunction">
<dt id="PyMarshal_WriteLongToFile">
void <tt class="descname">PyMarshal_WriteLongToFile</tt><big>(</big>long<em> value</em>, FILE<em> *file</em>, int<em> version</em><big>)</big><a class="headerlink" href="#PyMarshal_WriteLongToFile" title="Permalink to this definition">¶</a></dt>
<dd><p>Marshal a <tt class="xref docutils literal"><span class="pre">long</span></tt> integer, <em>value</em>, to <em>file</em>.  This will only write the
least-significant 32 bits of <em>value</em>; regardless of the size of the native
<tt class="xref docutils literal"><span class="pre">long</span></tt> type.</p>
<p>
<span class="versionmodified">Changed in version 2.4: </span><em>version</em> indicates the file format.</p>
</dd></dl>

<dl class="cfunction">
<dt id="PyMarshal_WriteObjectToFile">
void <tt class="descname">PyMarshal_WriteObjectToFile</tt><big>(</big><a title="PyObject" class="reference external" href="structures.html#PyObject">PyObject</a><em> *value</em>, FILE<em> *file</em>, int<em> version</em><big>)</big><a class="headerlink" href="#PyMarshal_WriteObjectToFile" title="Permalink to this definition">¶</a></dt>
<dd><p>Marshal a Python object, <em>value</em>, to <em>file</em>.</p>
<p>
<span class="versionmodified">Changed in version 2.4: </span><em>version</em> indicates the file format.</p>
</dd></dl>

<dl class="cfunction">
<dt id="PyMarshal_WriteObjectToString">
<a title="PyObject" class="reference external" href="structures.html#PyObject">PyObject</a>* <tt class="descname">PyMarshal_WriteObjectToString</tt><big>(</big><a title="PyObject" class="reference external" href="structures.html#PyObject">PyObject</a><em> *value</em>, int<em> version</em><big>)</big><a class="headerlink" href="#PyMarshal_WriteObjectToString" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a string object containing the marshalled representation of <em>value</em>.</p>
<p>
<span class="versionmodified">Changed in version 2.4: </span><em>version</em> indicates the file format.</p>
</dd></dl>

<p>The following functions allow marshalled values to be read back in.</p>
<p>XXX What about error detection?  It appears that reading past the end of the
file will always result in a negative numeric value (where that&#8217;s relevant), but
it&#8217;s not clear that negative values won&#8217;t be handled properly when there&#8217;s no
error.  What&#8217;s the right way to tell? Should only non-negative values be written
using these routines?</p>
<dl class="cfunction">
<dt id="PyMarshal_ReadLongFromFile">
long <tt class="descname">PyMarshal_ReadLongFromFile</tt><big>(</big>FILE<em> *file</em><big>)</big><a class="headerlink" href="#PyMarshal_ReadLongFromFile" title="Permalink to this definition">¶</a></dt>
<dd>Return a C <tt class="xref docutils literal"><span class="pre">long</span></tt> from the data stream in a <tt class="xref docutils literal"><span class="pre">FILE*</span></tt> opened for
reading.  Only a 32-bit value can be read in using this function, regardless of
the native size of <tt class="xref docutils literal"><span class="pre">long</span></tt>.</dd></dl>

<dl class="cfunction">
<dt id="PyMarshal_ReadShortFromFile">
int <tt class="descname">PyMarshal_ReadShortFromFile</tt><big>(</big>FILE<em> *file</em><big>)</big><a class="headerlink" href="#PyMarshal_ReadShortFromFile" title="Permalink to this definition">¶</a></dt>
<dd>Return a C <tt class="xref docutils literal"><span class="pre">short</span></tt> from the data stream in a <tt class="xref docutils literal"><span class="pre">FILE*</span></tt> opened for
reading.  Only a 16-bit value can be read in using this function, regardless of
the native size of <tt class="xref docutils literal"><span class="pre">short</span></tt>.</dd></dl>

<dl class="cfunction">
<dt id="PyMarshal_ReadObjectFromFile">
<a title="PyObject" class="reference external" href="structures.html#PyObject">PyObject</a>* <tt class="descname">PyMarshal_ReadObjectFromFile</tt><big>(</big>FILE<em> *file</em><big>)</big><a class="headerlink" href="#PyMarshal_ReadObjectFromFile" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a Python object from the data stream in a <tt class="xref docutils literal"><span class="pre">FILE*</span></tt> opened for
reading.  On error, sets the appropriate exception (<a title="exceptions.EOFError" class="reference external" href="../library/exceptions.html#exceptions.EOFError"><tt class="xref docutils literal"><span class="pre">EOFError</span></tt></a> or
<a title="exceptions.TypeError" class="reference external" href="../library/exceptions.html#exceptions.TypeError"><tt class="xref docutils literal"><span class="pre">TypeError</span></tt></a>) and returns <em>NULL</em>.</p>
</dd></dl>

<dl class="cfunction">
<dt id="PyMarshal_ReadLastObjectFromFile">
<a title="PyObject" class="reference external" href="structures.html#PyObject">PyObject</a>* <tt class="descname">PyMarshal_ReadLastObjectFromFile</tt><big>(</big>FILE<em> *file</em><big>)</big><a class="headerlink" href="#PyMarshal_ReadLastObjectFromFile" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a Python object from the data stream in a <tt class="xref docutils literal"><span class="pre">FILE*</span></tt> opened for
reading.  Unlike <a title="PyMarshal_ReadObjectFromFile" class="reference internal" href="#PyMarshal_ReadObjectFromFile"><tt class="xref docutils literal"><span class="pre">PyMarshal_ReadObjectFromFile</span></tt></a>, this function assumes
that no further objects will be read from the file, allowing it to aggressively
load file data into memory so that the de-serialization can operate from data in
memory rather than reading a byte at a time from the file.  Only use these
variant if you are certain that you won&#8217;t be reading anything else from the
file.  On error, sets the appropriate exception (<a title="exceptions.EOFError" class="reference external" href="../library/exceptions.html#exceptions.EOFError"><tt class="xref docutils literal"><span class="pre">EOFError</span></tt></a> or
<a title="exceptions.TypeError" class="reference external" href="../library/exceptions.html#exceptions.TypeError"><tt class="xref docutils literal"><span class="pre">TypeError</span></tt></a>) and returns <em>NULL</em>.</p>
</dd></dl>

<dl class="cfunction">
<dt id="PyMarshal_ReadObjectFromString">
<a title="PyObject" class="reference external" href="structures.html#PyObject">PyObject</a>* <tt class="descname">PyMarshal_ReadObjectFromString</tt><big>(</big>char<em> *string</em>, Py_ssize_t<em> len</em><big>)</big><a class="headerlink" href="#PyMarshal_ReadObjectFromString" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a Python object from the data stream in a character buffer containing
<em>len</em> bytes pointed to by <em>string</em>.  On error, sets the appropriate exception
(<a title="exceptions.EOFError" class="reference external" href="../library/exceptions.html#exceptions.EOFError"><tt class="xref docutils literal"><span class="pre">EOFError</span></tt></a> or <a title="exceptions.TypeError" class="reference external" href="../library/exceptions.html#exceptions.TypeError"><tt class="xref docutils literal"><span class="pre">TypeError</span></tt></a>) and returns <em>NULL</em>.</p>
</dd></dl>

</div>


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